Effectiveness of aquatic phytoremediation of nutrients via watercress (Nasturtium officinale), basil (Ocimum basilicum), dill (Anethum graveolens) and lettuce (Lactuca sativa) from effluent of a flow-through aquaculture operation

Abstract

Effluent from the aquaculture industry is a source of nutrient loading upon water bodies nationwide. Aquaponics, the simultaneous cultivation of fish and plants, has the potential to effectively reduce nutrient concentrations through phytoremediation, with the added benefit of producing a valuable crop. The purpose of this preliminary research was to determine if watercress ( Nasturtium officinale) could be used to reduce nutrients from aquaculture effluent in sufficient concentrations to be functional as a remediation technique. Additionally, basil (Ocimum basilicum), dill (Anethum graveolens) and lettuce (Lactuca sativa) were correspondingly examined. Conditions which affected plant growth versus nutrient remediation were also to be established. These conditions include the effects of water velocity and plant density as they pertain to nutrient uptake and plant growth. Tentatively, the lowest water velocity and highest plant density should provide the greatest potential for uptake of nutrients via the plants in the system.;Effluent from an existing aquaculture operation, rearing brook trout (Salvelinus fontinalis), was distributed to an aquatic phytoremediation system consisting of twelve experimental channels used for the cultivation of the plants. The dimensions for each channel were 243 cm long, 30 cm wide and 15 cm deep. Experimental treatments, varying by plant density and water velocity conditions, were implemented throughout the system. Plant densities of 0.04, 0.09 and 0.16 plants/cm2 and water velocities of 0.61, 0.30 and 0.061 cm/s were alternatively combined to create nine experimental treatments. Effluent samples were taken, from the aquaculture operation and the end of each channel, every three weeks throughout three consecutive studies conducted over a total period of thirteen months. Water samples were analyzed in the laboratory for ammonia, nitrate, nitrite and phosphate.;No statistically significant differences existed between the experimental treatments throughout each study of the aquaponics research. Some operational conditions were established through notable trends within the results. The low velocity low density treatment was most effective at the removal of nitrate and phosphate via watercress. The low velocity high density treatment was most effective at the removal of phosphate via watercress. The low velocity high density treatment was most effective at the removal of ammonia via lettuce. The watercress cultivated in the high velocity high density treatment resulted in greater plant biomass and height. The average total percent nutrient removals achieved via the plants did not exceed 11.2%. Significant reductions throughout the aquaponic system may not have occurred due to initially low nutrient concentrations, insufficient plant biomass and/or densities, inadequate light intensity or environmental temperatures, or short contact times between constituents and plants

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